High pressure electric discharge device with getter of barium perioxide and copper

ABSTRACT

Barium peroxide and copper are disposed within a high pressure electric discharge device to getter hydrogen entrapped therein and reduce the concentration of liberated oxygen. In one embodiment, powdered barium peroxide is held in a nickel cup; a layer of copper filings is disposed above and separated from the barium peroxide by a pad of fibrous aluminum silicate material; and the cup is capped with a disc of porous stainless steel. The getter is disposed in the device at a location where it will be subjected to ambient operating temperatures between about 150* and 360* C.

United States Patent [191 Waymouth et al.

[ 1 June 5, 1973 HIGH PRESSURE ELECTRIC DISCHARGE DEVICE WITH GETTER OF BARIUM PEROXIDE AND COPPER lnventorszJohn F. Waymouth; William M. Keeffe; W. Calvin (iungle, all of Danvers, Mass.

Assignee: GTE Sylvania Incorporated, Danvers, Mass Filed: July 13, 1972 Appl. No.: 271,401

U.S. Cl ..3l3/l74, 252/l8l.l Int. Cl. ..H0lj 61/24 Field of Search ..313/174 References Cited UNITED STATES PATENTS 7/1970 Gungle et al. ..3l3/184 Primary Examiner-Roy Lake Assistant Examiner-Darwin R. Hostetter Attorney-Norman J. OMalley. Edward J. (oleman and Joseph C. Ryan [57] ABSTRACT Barium peroxide and copper are disposed within a high pressure electric discharge device to getter hydrogen entrapped therein and reduce the concentration of liberated oxygen. In one embodiment, powdered barium peroxide is held in a nickel cup; a layer of copper filings is disposed above and separated from the barium peroxide by a pad of fibrous aluminum silicate material; and the cup is capped with a disc of porous stainless steel. The getter is disposed in the device at a location where it will be subjected to ambient operating temperatures between about 150 and 360 C.

13 Claims, 8 Drawing Figures .PATENTED JUN 5 I973 SHEET 1 OF 3 PATENTED RE IGNITION VOLTAGE SHEET 3 OF 3 A N0 GETTER 2-8002 ONLY ADM|XTURE OF B002 +Cu D- B002+Cu SCREENS E- B002+Cu FILINGS SEPARATED BAO BA(OH)2 4 HOURS FIG.7

(BAO) (0 @f HEAT (Cu)+(H O) -T@ +6 (CuOH) FIG.8

HIGH PRESSURE ELECTRIC DISCHARGE DEVICE WITH GETTER F BARIUM PERIOXIDE AND COPPER BACKGROUND OF THE INVENTION This invention relates to high pressure electric discharge devices, such as mercury or metal halide arc lamps, and particularly to the means for gettering hydrogen in such lamps.

High pressure discharge devices generally comprise a quartz arc tube containing a fill of mercury or mercury and metal halides and which is supported by a wire frame within an outer bulbous envelope containing an inert gas such as nitrogen. It is well known that hydrogen contamination is detrimental to the operation of such devices. When trapped within the bulbous envelope, the hydrogen diffuses through the quartz wall of the arc tube and adversely affects both starting and reignition voltages. The hydrogen migrates into the arc tube and forms in the case of iodine fills, hydrogen iodide, which is a volatile iodine containing species and exists as a gas at temperatures even as low as -F. At low ambient temperatures, the effect of hydrogen contamination is especially noticeable because the presence of the corresponding iodide produces high starting voltages. Moreover the presence of hydrogen iodide in the arc tube results in a high value of voltage required to reignite the lamp each half cycle of altemating current during the warm-up phase of the lamp operation. This voltage, referred to hereafter as reignition voltage, is an important parameter in determining whether a lamp can operate reliably on a given ballast circuit. The lower it is, the more reliable will be operation, or conversely the more economical will be the ballast design to reach a desired level of reliablilty.

One of the sources of hydrogen in such devices is the bulbous envelope. Ultraviolet light emitted from the arc tube releases hydrogen from hydroxyl radicals which are entrapped in the glass jacket.

Getters, that is materials which entrap extraneous gases, have previously been utilized in such devices. Gettering, as usually practiced in the art, involves flashing or volatizing barium metal to react with gases, thereby removing them from the system. However, such procedures not only remove the hydrogen, but also getter the nitrogen which is intentionally added. Since an inert gas should generally be present within the envelope, replacement of the nitrogen with argon would be required, as argon is not gettered by barium. But because the use of argon reduces the potential where arcing between elements of the lamp can occur, it is not as satisfactory as nitrogen. Thus, the use of conventional barium getters has serious disadvantages. The same is true of the so-called flashless getters, such as tantalum, cerium, or alloys containing these metals, such as are known to the art. All of these react rapidly with nitrogen as well as hydrogen and would require replacement of the nitrogen fill gas of the outer jacket by argon.

A method of removing hydrogen from the outer jacket, without appreciably affecting the nigrogen content, is described by U.S. Pat. No. 3,519,864, assigned to the assignee of the present application. This patent employs barium peroxide as the getter and disposes the material at a location in the outerjacekt where the temperature is normally expected to lie between 150 and 427C. Within this temperature range, barium peroxide selectively getters hydrogen by the reaction The gettering rate at a hydrogen pressure of 30 torr for 0.7 grams of BaO is 25 millitorr-liter/minute at a temperature of 300C. However, at this temperature, the reaction results in an oxygen equilibrium partial pressure of 0.2 millitorr. Such a partial pressure of oxygen is objectionable on several counts. First, nickel plated frame parts begin to show evidence of oxidation after about hours of lampbperation, which could lead to weld failures and presents a generally unsightly appearance. Secondly, the molybdenum arc tube leads show the formation of the white cyrstalline form, molybdenum trioxide after about 100 hours which could lead to failure of the hermetic molybdenum ribbon seal resulting in an arc tube leaker. Thirdly, the liberated oxygen may make the identification of outer jacket leakers difficult in manufacture.

SUMMARY OF THE INVENTION In view of the aforementioned shortcomings of the prior art, it is an object of this invention to provide an improved high pressure electric discharge device having means for effectively gettering hydrogen in a selective manner without producing the deleterious effects associated with the release of oxygen.

In a study of alternative getters, we have found, quite unexpectedly, that an admixture of copper and barium peroxide eliminates hydrogen more efficiently than either of these substances separately. We further find that the liberated oxygen is reduced in concentration to such an extent as to eliminate the difficulties of misidentification of outer jacket leakers in the manufacturing process, and to eliminate the observed formation of molybdenum trioxide. Further, we have experienced no noticeable reactions between nitrogen gas fill and the getter package.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully described in the following detailed description in conjunction with the accompanying drawings, in which:

FIG. 1 is an elevational perspective view of a high pressure metal iodide discharge lamp having a getter arrangement in accordance with the invention;

FIG. 2 is a plan view of a first getter package embodiment according to the invention;

FIG. 3 is a sectional elevation of the getter package of FIG. 2;

FIG. 4 is a plan view of a second getter package embodiment according to the invention;

FIG. 5 is a sectional elevation of the getter package of FIG. 4;

FIG. 6 is a sectional elevation of a third getter package embodiment according to the invention;

FIG. 7 is a graph of reignition voltage as a function of lamp aging which shows curves for various getter package embodiments; and

FIG. 8 is a schematic diagram illustrating the reactions involving the getter materials and hydrogen.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, the lamp includes a generally tubular outer bulbous envelope 1 having a bulbous central portion and a conventional base 14 attached to the bottom thereof. Extending inwardly from the base and inside of the envelope 1 is a mount 15 having a pair of stiff lead-in wires 12 and 16 in electrical conducting relation with the base 14. Disposed upon one of the stiff lead-in wires 12 is a lower U-shaped support 8 welded thereto. The U-shaped support 8 comprises a pair of vertical wires 23 and 24 rising from a horizontal base wire 25. The upper ends of the lower U-shaped support 8 are welded together with a lower metal strap 7 which in turn supports a quartz glass arc tube 2. Preferably, the lower metal strap includes two sections abutting against either side of the arc tube 2 thereby holding it firmly in place and touching only the press seal 30 of the arc tube and not the body. Generally, both sides of the lower strap 7 can be of identical construction. A pair of bumpers 26 are welded to the lower U-shaped support 8 and abut against the tubular portion of walls of the outer-bulbous envelope 1, thereby stabilizing the structure within the lamp. Preferably, these bumpers are made of a resilient material so that if the lamp is jarred, they will absorb much of the shock.

Since the lower U-shaped support 8 is electrically connected to the stiff lead-in wire 12, the support 8 forms part of the circuit in the device. Current passes from the base 14 into the lower U-shaped support 8 and thence to lead-in wire 21 which in turn is connected to an electrode 4 in the arc tube. It is sometimes desirable to place an insulating shield about the lead-in wire 21 to prevent arcing within the lamp and between the various elements. Current passes from the lead-in wire 21 to the electrode 4 through an intermediary lead-in wire 29 and molybdenum foil section 6.

The other side of the circuit is formed through the stiff lead-in wire 16 which is preferably bent out of place so that the parts on one side of the line are insulated from those on the other side. A resistor 13 is attached to the stiff lead-in wire 16 and thence to a connector 27 which in turn leads through a lead-in wire 31 and molybdenum foil section 6 to a starting probe 5. A bimetal 22 is attached to the lead-in wire 29 which is connected to the electrode 4. The bimetal 22 is biased open when the device is turned off, but upon starting, it biases closed against the lead-in wire 31 to the probe 5, thereby establishing the same current potential at the probe and the electrode 4. Such closing prevents electrolysis between the probe and electrode.

At the other end of the arc tube 2, an upper support is mounted within the tubular portion of the bulbous envelope 1. The support frame 10 includes a horizontal section 18 having vertical supports 17 and 19 depending downwardly therefrom and attached at the free ends to an upper metal strap 11 which surrounds the press seal 40 of arc tube 2 and rigidly holds it in place. Preferably, the construction and disposition of upper metal strap 11 is similar to lower strap 7. A pair of upper bumpers 9 are mounted upon the vertical sections 17 and 19 of the upper support 10 and resiliently abut against the sides of the tubular portion of the bulbous envelope 1. Such disposition prevents breakage of the lamp if the arc tube is shaken or dropped.

A lead-in wire 28 extends to the outside of the arc tube 2 and is attached at its inner end to a molybdenum foil section 6 and thence to an electrode 3. An electrical connection is made between stiff lead-in wire 16 and lead-in wire 28 through a thin conducting lead 20 which may be of any suitable conducting material. Preferably, the conducting lead 20 is as distantly removed from the arc tube 2 as possible, generally by bending it around the perimeter of the outer bulbous envelope 1.

The envelope 1 of the lamp is filled with nitrogen at a pressure of about half an atmosphere at room temperature to minimize the occurrence of arc-overs between the electrical conductors therein, beneficially effect the temperature distribution over the arc tube 2, and reduce photoelectric current flowing to the arc tube.

In accordance with the invention, a getter package 34 containing barium peroxide and copper is attached to the upper support 10 by means of mounting straps 36 and 38 welded to vertical supports 17 and 19, respectively. At this preferred location, the getter package is not in the direct path of ultraviolet light generated by the arc tube 2 and is disposed in an area where the ambient operating temperature is between about and 360C when the lamp is operated horizontally, or vertically with the base 14 up.

Getter package 34 may be implemented in a variety of ways provided it retains the barium peroxide and copper, permits gas in the envelope to react with the barium peroxide and copper, and substantially prevents the penetration of ultraviolet light through to the barium peroxide. FIGS. 2-6 illustrate three getter package emobdiments which have been constructed and tested.

FIGS. 2 and 3 show a preferred embodiment of getter package 34 wherein a quantity of powdered barium peroxide 40 is held in a nickel cup 42, having a thin strip of nickel welded to the bottom thereof to provide mounting straps 36 and 38. A pad 44 of fibrous aluminum silicate material, such as is available as Fiberfrax from the Carborundum Corp. of Buffalo, N.Y., is placed above the layer of powdered barium perioxide. Disposed above the fibrous pad 44, and thereby separated from the barium peroxide, is a layer of copper filings 46. The inert fibrous pad 44 prevents physical intermixture of the barium peroxide powder and copper filings but does not inhibit gas flow through both substances. Finally, the package is capped with a disc 48 of porous stainless steel which acts as a semipermeable membrane preventing the contents from falling out of the package but yet not inhibiting gas flow, particularly hydrogen gas, into the package to react with the copper and barium peroxide. In addition, of course, the porous stainless steel disc 48 is substantially opaque to ultraviolet light. The disc 48 may be secured in place by a slight roll over 50 of the nickel cup. In a specific embodiment, the cup 42 was formed from a 0.005 inch thick sheet of nickel, and stainless steel disc 48 had a 5 micron porosity.

In the embodiment of FIGS. 4 and 5, the nickel cup 42 contains a quantity of powdered barium peroxide 40 which is retained in the package by a cap comprising a plurality of layers of copper screening 52. The screening, which also may be secured by a cup roll-over 50, is fine enough to prevent the barium peroxide powder from falling out of the package but does not inhibit gas flow. The holes in the layers of screening are not in alignment and thus, substantially prevent the penetration of ultraviolet light. In a specific embodiment, five layers of I mesh copper screening were employed.

FIG. 6 shows an embodiment wherein an admixture 54 of barium peroxide powder and copper filings is retained in nickel cup 42 by porous stainless steel disc 48.

Results of an accelerated life test experiment designed to evaluate the above described getter package embodiments as compared to a prior art getter package are illustrated by the curves of FIG. 7. These curves represent measurements of the reignition voltage as a function of lamp aging. The value of 50 volts for this reignition voltage is quite typical for well processed lamps after aging; the increase which is subsequently observed is due entirely to the permeation of hydrogen from the outer jacket into the arc tube forming the aforementioned hydrogen iodide. The magnitude of the reignition voltage being approximately proportional to thequantity of hydrogen iodide formed, which is in turn determined by the excess pressure of hydrogen outside the arc tube driving hydrogen in, the magnitude of the reignition voltage becomes a measure of the residual ungettered pressure of hydrogen in the outer jacket. The lower the rate of climb and the lower the peak value of the measured reignition voltage in this accelerated test, the more effective has been the outer jacket gettering means in reducing an added 2.5 torr of hydrogen to negligible values; In each case a 1,000 watt metal halide lamp was employed having a jacket fill comprising nitrogen at 365 torr, contamination with 2.5 torr of hydrogen. Curve (A) was obtained with no getter in the lamp. Curve (B) represents the data obtained using a prior art type getter package comprising a nickel cup filled only with 0.7 grams of powdered barium peroxide, and capped with a porous stainless steel disc. Curve (C) was obtained using the package of FIG. 6 containing an admixture of 0.7 grams of barium peroxide powder and 0.3 grams of copper filings. Curve (D) was obtained for the getter package of FIGS. 4 and 5 containing 0.7 grams of powdered barium peroxide retained by five layers of 100 mesh copper screening. Curve (E) represents the data obtained using the getter package of FIGS. 2 and 3, wherein 0.7 grams of powdered barium peroxide and 0.3 grams of copper filings are separated by a fibrous pad.

Results for no getter (A) and plain barium peroxide getter (B) are seen to follow well known trends. The addition of copper, on the other hand, yielded unexpected results. In all cases (C,D and E) the copper appears to have increased the hydrogen gettering rate of the package. The embodiment consisting of the layer of copper filings above and separated by a fibrous pad from the barium peroxide(FIGS. 2 and 3) resulted in the lowest reignition voltage spikes (curve E of FIG. 7). While mixing the barium peroxide and copper together gave higher spikes than curve (E), the reignition voltages of curve (C) are still much lower than curve (B), thereby representing a significant improvement over the use of barium peroxide alone. This suggests that while the copper may be reducing the barium peroxide when mixed together, another reaction takes place, whenever copper is present, which getters hydrogen.

Referring to the schematic diagram of FIG. 8, we have postulated that the following reactions take place:

L 8210, Hg 6 which is the basic hydrogen gettering process by the barium peroxide forming barium hydroxide as the roduct;

2. BaO BaO 0 which is the thermal reduction of barium peroxide forming barium oxide and oxygen;

3. 2Cu 9% O Cu O wherein the oxygen liberated in reaction 2 oxides the copper to form cuprous oxide;

4. C1110 Hz 2Cu i H2O wherein the cuprous oxide formed by reaction 3 is reduced in this second hydrogen gettering process, which recycles the copper back to the elemental form;

5. Bao H O Ba(OI-I) in which the water vapor formed in reaction 4 is picked up by the barium oxide formed in reaction 2 to form barium hydroxide as a product; and 6. Cu O H k 0 2CuOH which is a third hydrogen gettering process forming cuprous hydroxide. Since this product is only stable up to 360C, it is preferred, that the ambient temperature of the getter package be maintained below this limit.

As indicated by the above reactions, the BaO Cu getter not only provides a more effective hydrogen getter, but it also substantially reduces the concentration of liberated oxygen. This was demonstrated by observation of the lamp structure after the aforementioned aging experiments. The usual corrosion formation on metal parts was substantially reduced, and we observed no formation of molybdenum trioxide. Further, no difficulty has been experience in identifying jacket leakers in the manufacturing process.

Although the invention has been described with re spect to specific embodiments, it will be apprecaited that modifications and changes may be made by those skilled in the art without departing from the true spirit and scope of the invention. For example, porous disc 48 may comprise a foraminous plate of corrosionresistant material other than stainless steel which is gaspermeable, but substantially impermeable to particulate matter, and which is substantially opaque to ultraviolet light. Also, pad 44 may comprise a material other than fibrous aluminum silicate, provided the material is inert and gas-permeable, but substantially impermeable to particulate matter. Further, a porous disc of sintered copper may be used in the embodiment of FIGS. 4 and 5, in lieu of the layers of copper screening 52. In addition, whereas the specific embodiment described is a getter package containing barium peroxide and copper, it is contemplated that the copper may be replaced by any material having similar oxidation properties to those of copper.

What we claim is:

l. A high pressure electric discharge device comprising: a bulbous glass envelope; a quartz glass arc tube disposed within said bulbous envelope; means to form an electric discharge within said arc tube; and hydrogen getter means disposed within said bulbous envelope, said getter means comprising barium peroxide and copper.

2. A device according to claim I wherein said getter means is disposed in a location in said device wherein it is subjected to operating temperatures between about and 360C.

3. A device according to claim 1 wherein said getter means comprises a package containing said barium peroxide and copper, said package being substantially opaque to ultraviolet light.

4. A device according to claim 3 further including means supporting said are tube within said envelope,

and wherein said getter package has mounting straps whereby it is attached to said supporting means at a location wherein it is subjected to operating temperatures between about 150 and 360C, said barium peroxide and copper reacting at said operating temperatures to substantially getter any hydrogen present in said envelope and to substantially reduce the concentration of liberated oxygen.

5. A device according to claim 3 wherein said getter package comprises a cup containing an admixture of powdered barium peroxide and copper filings, said cup being capped w1th a (1186 of porous material.

6. A device according to claim 3 wherein said getter package comprises a cup containing a quantity of powdered barium peroxide, said cup being capped with a porous body of copper.

7. A device according to claim 6 wherein said porous body of copper comprises a plurality of layers of copper screening.

8. A device according to claim 7 wherein each of said layers of screening is about lOO mesh.

9. A device according to claim 8 wherein said cup is capped with five layers of said copper screening.

12. A device according to claim ll wherein said getter package is disposed in a location in said device wherein it is subjected to operating temperatures between about ISO and 360C.

13. A device according to claim 12 further including means supporting said are tube within said envelope, and wherein said getter package has mounting straps whereby it is attached to said supporting means, said barium peroxide and copper reacting at said operating temperatures to substantially getter any hydrogen present in said envelope and to substantially reduce the concentration of liberated oxygen. 

2. A device according to claim 1 wherein said getter means is disposed in a location in said device wherein it is subjected to operating temperatures between about 150* and 360*C.
 3. A device according to claim 1 wherein said getter means comprises a package containing said barium peroxide and copper, said package being substantially opaque to ultraviolet light.
 4. A device according to claim 3 further including means supporting said arc tube within said envelope, and wherein said getter package has mounting straps whereby it is attached to said supporting means at a location wherein it is subjected to operating temperatures between about 150* and 360*C, said barium peroxide and copper reacting at said operating temperatures to substantially getter any hydrogen present in said envelope and to substantially reduce the concentration of liberated oxygen.
 5. A device according to claim 3 wherein said getter package comprises a cup containing an admixture of powdered barium peroxide and copper filings, said cup being capped with a disc of porous material.
 6. A device according to claim 3 wherein said getter package comprises a cup containing a quantity of powdered barium peroxide, said cup being capped with a porous body of copper.
 7. A device according to claim 6 wherein said porous body of copper comprises a plurality of layers of copper screening.
 8. A device according to claim 7 wherein each of said layers of screening is about 100 mesh.
 9. A device according to claim 8 wherein said cup is capped with five layers of said copper screening.
 10. A device according to claim 3 wherein said getter package comprises a cup containing a quantity of powdered barium peroxide and a layer of copper filings separated from the barium peroxide by a pad of inert material which is gas-permeable but substantially impermeable to particulate matter, said cup being capped with a disc of porous material.
 11. A device according to claim 10 wherein said cup is nickel, said pad is fibrous aluminum silicate, and said porous disc is stainless steel.
 12. A device according to claim 11 wherein said getter package is disposed in a location in said device wherein it is subjected to operating temperatures between about 150 and 360*C.
 13. A device according to claim 12 further including means supporting said arc tube within said envelope, and wherein said getter package has mounting straps whereby it is attached to said supporting means, said barium peroxide and copper reacting at said operating temperatures to substantially getter any hydrogen present in said envelope and to substantially reduce the concentration of liberated oxygen. 